Charging system update, Mk-V

[Jeffbo1]

Well my mechanic and I have tried various things to see if the dynamo is charging the battery and to no avail. We have added a new ground strap at the battery and have all the electrics tight, all circuits solid and the lighting is working flawlessly. But it still appears we are running off the battery. No voltage returning to the battery. So the dynamo must be at fault. Any thoughts on what to look for or test in this regard? Hopefully just a bad brush set etc. but not sure what to do to get her to charge the battery....Jeff

[David Lawrence]

Jeff,
Regarding your charging problem, have you tried diconnecting the battery and checking if the lights work on direct power from the dynamo? Be careful if it does work not to overrev the motor, if the dynamo is working it will be putting out more than 6v so could blow those rather rare 6v bulbs!.
If the dynamo is working the problem will be in the CVC box, (the voltage regulator) these are rather temperamental and if it is not working I suggest you replace it with a modern solid state version, these are available and can be obtained in a very similar looking case to the original.
The final check if you have not already tried is to remove the dynamo and put 6v into it, if the windings are good the it should motor, be careful it can recoil strongly if held in the hand.
I assume you have checked the brushes and commutator arm for wear and grease, or verdigris if the bike has been standing.
Dave

[Jeffbo1]

Thank you Dave, I will forward your information to my mechanic...many thanks pal!

Jeff

[Vermont-Ian]

Assuming that the dynamo runs as a motor when you close the cutout by hand with the 6V battery in circuit, it could be absence of residual magnetism in the filed coil,  On my Mk III that pesky Lucas dynamo often doesn't work if the bike has been standing for a few months.  Sometimes it's just dirty contacts in the regulator (cut-out or voltage regulation contacts).  Sometimes after standing a longer time it's loss of residual field in the dynamo (the magnet that the field coil is wound around).  Spinning the dynamo by hand should generate a volt or two on a voltmeter connected between the 'D' terminal and the body.  If not, instill  some residual magnetism by hooking up the field coil to a 12 volt battery between 'F' and the body to give it a jolt (a hammer jolt can also be helpful).  Connect the 12V with the same positive or negative earth that the bike is set up for (I think).  Then disconnect the 12 V and check the volts again when you spin by hand (in the direction that it's turned by the engine).  If the polarity is wrong, you connected the 12V to the field coil the wrong way.  If so, reconnect the other way and repeat.    Have fun, if that's possible with Lucas electrics.

[Jeffbo1]

Thank you Ian, I have forwarded your comments to my mechanic....hopefully we'll get to the bottom of this mystery....it's gotta be either the magnetism of the dynamo, or lack there of, or it's something in the voltage regulator....many thanks again!

Jeff